Patent GB-822027-A (GB)
Title: Method of monitoring the color of a fluid bath
IPC: G01J3/46
Filed: 1956-03-07
Abstract: 822,027. Comparing colours. PROCTOR & SCHWARTZ Inc. March 7, 1956 [March 9, 1955], No. 7137/56. Class 97(1) [Also in Group XL(b)] A method monitoring the colour intensity of a fluid bath comprises selecting a sample from the bath, constantly replacing the sample from the bath, sequentially selecting a plurality of limited frequency bands for a beam of light, passing the beam through a standard, splitting the beam into two beams and adjusting the standard so that the transmissions in one beam simulate those through the desired fluid, passing the other beam through the sample and continuously comparing the intensities of the resultant beams. As shown in Fig. 1, the device comprises a source of light 10, a collimator 11 a rotatable disc 13 bearing three differently coloured filters 27, 28, 29 (Fig. 4), a variable polarization device 14, and a Wollaston prism 15 dividing the coloured beam into a beam A directed through a cell 19 containing the fluid to be observed and a beam B passing through an aperture 21. A polarizer 16 is continuously rotated so that the intensities of the beams A and B vary sinusoidally with a phase difference of 90 degrees and the two beams fall upon a screen after reflection by prisms 22, 23, any variations in the illumination of the screen due to differences in intensity between the beams A and B being detected by a photo-cell 25 and a circuit 26 which indicates the variation of the colour of the fluid from the standard and, if desired, automatically corrects it by causing dye to be added. The polarizing device 14 is rotated to a certain position for each colour so that the plane of polarization of the light falling on the prism 15 is varied accordingly and so the intensity of the beam B is adjusted for each colour to correspond to that of the standard colour desired. To allow this adjustment to be effected automatically a plane polarizer 30, Fig. 4 is mounted in a ring 52 rotatable about a tube 30 and having an extension 55 carrying an adjusting screw 56. Rotatable coaxially with the ring 52 is a ring 48 having an extension 53 bearing a pin 54 pressed against the screw 56 by a spring 57. The two rings are urged counterclockwise by a spring 60, their angular position, and so that of the polarizer 30, being determined by the engagement of a stop pin 72, Fig. 3, on the extension 53 with a stop on one of three rings 41, 42, 43 rotatable coaxially with the ring 52. The angular position of the rings 41, 42, 43 is adjustable by means of micrometers 34, 35, 36, which engage respectively stops 77, 78 and 76 on the rings. To ensure that only the appropriate ring is in operation when a particular colour filter is in use the shaft 80 of the filter disc 13 is connected to a shaft 79 having three cams 84, 85, 86 respectively engaged by rollers on arms 90, 91. 92 pivoted respectively to the rings 41. 42..43 so that the two rings not in use are rotated by the cams and arms so as to be free of the micrometer stops, as shown in Fig. 4 when the pin 72 engages the stop on the remaining ring which therefore determines the angular position of the polarizer 30 and thence the intensity of that colour in the beam B.